The mixture of organoclays and polyolefins, commonly called polyolefin nanocomposites, is highly desired because organoclays can add stiffness and toughness to polyolefin-containing compounds. Polyolefins for plastic structures have been useful since the mid-20th Century. Organoclays, smectite inorganic clays intercalated with organic ions, such as quaternary ammonium, have become useful in the last decade.
The UV stabilization of nanocomposites has shown to be difficult when not in black or grey colors, typical of hard to stabilize polymers. Initial results showed large changed in color (Delta E or ΔE) very quickly, and “crazing” at low exposure times.
As explained in Wikipedia, crazing is one phenomenon that frequently precedes fracture in some glassy thermoplastic polymers. Associated with crazes are regions of very localized yielding, which lead to the formation of small and interconnected microvoids. Fibrillar bridges form between these microvoids wherein molecular chains become oriented. If the applied tensile load is sufficient, these bridges elongate and break, causing the microvoids to grow and coalesce; as the microvoids coalesce, cracks begin to form.
A craze is different from a crack in that it can support a load across its face. Furthermore, this process of craze growth prior to cracking absorbs fracture energy and effectively increases the fracture toughness of the polymer. Crazes form at high stressed regions associated with scratches, flaws, and molecular inhomogeneities: in addition they propagate perpendicular to the applied tensile stress, and typically are 5 μm or less thick. It occurs mostly in amorphous, brittle polymers like polystyrene (PS), and polymethylmethacrylate (PMMA). The appearance of white color is caused by the presence of air in the craze.
Though polypropylene and thermoplastic polyolefins (TPOs) without organoclay are usually quite weatherable, with organoclay nanocomposite materials are much worse in UV performance.